title: HTLV-1 Tax oncoprotein subverts the cellular DNA damage response via binding to DNA-dependent protein kinase.
abstract: Human T-cell leukemia virus type-1 is the causative agent for adult T-cell leukemia. Previous research has established that the viral oncoprotein Tax mediates the transformation process by impairing cell cycle control and cellular response to DNA damage. We showed previously that Tax sequesters huChk2 within chromatin and impairs the response to ionizing radiation. Here we demonstrate that DNA-dependent protein kinase (DNA-PK) is a member of the Tax.Chk2 nuclear complex. The catalytic subunit, DNA-PKcs, and the regulatory subunit, Ku70, were present. Tax-containing nuclear extracts showed increased DNA-PK activity, and specific inhibition of DNA-PK prevented Tax-induced activation of Chk2 kinase activity. Expression of Tax induced foci formation and phosphorylation of H2AX. However, Tax-induced constitutive signaling of the DNA-PK pathway impaired cellular response to new damage, as reflected in suppression of ionizing radiation-induced DNA-PK phosphorylation and gammaH2AX stabilization. Tax co-localized with phospho-DNA-PK into nuclear speckles and a nuclear excluded Tax mutant sequestered endogenous phospho-DNA-PK into the cytoplasm, suggesting that Tax interaction with DNA-PK is an initiating event. We also describe a novel interaction between DNA-PK and Chk2 that requires Tax. We propose that Tax binds to and stabilizes a protein complex with DNA-PK and Chk2, resulting in a saturation of DNA-PK-mediated damage repair response.
authors.affiliation: Department of Microbiology and Molecular Cell Biology, Center for Biomedical Proteomics, Eastern Virginia Medical School, Norfolk, Virginia 23507, USA.
authors.forename: Sarah S
authors.initials: SS
authors.lastname: Durkin
authors.forename: Xin
authors.initials: X
authors.lastname: Guo
authors.forename: Kimberly A
authors.initials: KA
authors.lastname: Fryrear
authors.forename: Valia T
authors.initials: VT
authors.lastname: Mihaylova
authors.forename: Saurabh K
authors.initials: SK
authors.lastname: Gupta
authors.forename: S Mehdi
authors.initials: SM
authors.lastname: Belgnaoui
authors.forename: Abdelali
authors.initials: A
authors.lastname: Haoudi
authors.forename: Gary M
authors.initials: GM
authors.lastname: Kupfer
authors.forename: O John
authors.initials: OJ
authors.lastname: Semmes
mesh_terms: D034961:Antigens, Nuclear / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D064447:Checkpoint Kinase 2; D003593:Cytoplasm / Q000378:metabolism; D004249:DNA Damage; D004260:DNA Repair; D051747:DNA-Activated Protein Kinase / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism; D016356:Gene Products, tax / Q000378:metabolism*; D015368:Human T-lymphotropic virus 1 / Q000378:metabolism*; D006801:Humans; D000072200:Ku Autoantigen; D008856:Microscopy, Fluorescence / Q000379:methods; D008954:Models, Biological; D009154:Mutation; D010766:Phosphorylation; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism
chemical_list: D034961:Antigens, Nuclear; D004268:DNA-Binding Proteins; D016356:Gene Products, tax; D064447:Checkpoint Kinase 2; C578634:CHEK2 protein, human; D051747:DNA-Activated Protein Kinase; D017346:Protein Serine-Threonine Kinases; C000606509:Xrcc6 protein, human; D000072200:Ku Autoantigen